Electric heater



P. M. HULBERT.

ELECTRiC HEATER.

APPLICATION FILEDY on. 31, 1910. RENEWED JAN. 15.1919.

Patented Oct. 14,1919.

2 SHEETS-SHEET I.

P. M. HULBERT.

ELECTRIC HEATER.

APPLICATION FILED OCT. 31, 1910. RENEWED JAN Patented Oct. 14, 1919.

PRESCOTT M. HULBEBT, OF DETROIT,

ELECTRIC HEATER,

Specification of Letters Patent.

Patented Oct. 14, 1919.

Application filed October 31, 1910, Serial No. 589,938. Renewed January15, 1919. Serial No. 271,337.

To all whom it may concern:

Be it known that I, PREsco'rr M. HULBERT, a citizen of the United Statesof America, residing at Detroit, in the county of Wayne and State ofMichigan, have invented certain new, and useful Improvements in ElectricHeaters, of which the following is a specification, reference being hadtherein to transformed commercial electrical current.

Heretofore, various constructions of carployed for developing heat,buthave proven unsatisfactory for various causes among which are first,the combustible nature of the material when heated beyond the tem'perature of ignition, second, the varying resistance under differentconditions which render it diihcult to control the heat and currentconsumption, third the necessity for using a large current volume at lowpressure which requires the transformation of the 30V commercialcurrents available, fourth, the difficulty in fashioning the materialinto the desired form and spaced dimensions with the requisitemechanical strength and proper electrical resistance. For these andvarious other reasons carbon heating units are objectionable andunsatisfactory.

It is the object of the present invention,

first, to obtain a method of constructing carbon heating units of anydesired form and dimensions; and to impart to each unit an independentlyselected and predetermined electrical resistance according to theheating effect desired, second, to protect this unit from destructionthrough combustion and from xcessive heat and. at the same time-todeveloptherewith high ten'iperatures, third, to place the unit in anaccessible position so that the worlo may be conveniently inserted into"and renamed from the zone of high heat, fourth, to provide an effectiveheat insulation and to guard against loss of heat through com'ccliionwhen the heating cham; hm' is open. These and other objects areaccomplished y the construction as hereinafter describcdyy- I In thedrawings,

Figures 1 to 4 are diagrammatic perspective views illustrating themethod of constructing the carbon resistance element;

Figs. 5and 6 are similar views showing a modified construction;

Fig. 7 is a verticalcentral section through a protected unit designedfor furnace construction;

Figs. 8 and 9 are respectively longitudinal and cross section through amodified form of protected unit;

Fig. 10 is a section through another modification; 7

Figs. '11, 12, and 13 show modifed contructions of resistance elements;

Fig. 14 is a view similar to Fig. 7 of a modified furnace construction,

Fig. 15 is an elevation of the slitted unit having extended dead ends;

Fig. 16 is aperspective View of sectional units designed for arectangular furnace construction Fig. 17 is a horizontal section showingthe connection of the terminals to the resistance; and Fig. 18 is ahorizontal section of the resistance after the slitting and'beforeremoving the core.

My improved heating unit is constructed ofsubstantially pure carbon andthus differs from constructions in which mixtures of carbon and inertrefractory materials have been employed. Preferably I employ graphiticcarbon of that variety which has the electrical current. This slittingmay be I performed in various ways, but as shown in .Fig. 3, the tube orcylinder is slitted alternately from opposite ends C, C, the slits beinguniformly spaced and the series eX- tending completely around thecylinder, with terminal portions D, D of somewhat greater ection. Inslitting, the depth of t :2 cut is less than the thickness of the all ofthe cylinder and consequently all of the sections between the slits aretied together, and the rigidity of the cylinder is not impaired. Theslitted cylinder is then engaged with a suitable chuck or holder lil andis bored in a lathe or other tool. to remove the solid inner shell F,leaving the sections between the slits "tree from each other with theexception of the connection portions at opposite ends. As a result a zigbody is termed, the resistance of which is determined by the munber ofslits, and the selection of this resistance is not limited by reason ofthe original size or dimensions of the tubular body, but may be varied.as predetermined.

In place of slitting the body D longitudinally, it may be cut into aspiral form as shown at G Fig. 5, leaving the same uncut inner shell,and subsequently boring through this shell as shown in Fig. (3.

An electrical resistance formed as above described may be practicallyconstructed suitable for use with available con'm'iercial' currentswithout transformation to reduce the 'oltage. it however, such aresistance were to be heated above the ignition point and exposed to theatmosphere, it would soon be destroyed by combustion and even whereprotected by embedding in a body of refractory material the same resultwill follow after a greater length of time. in fact it has been foundpractically impossible to protect such a resistance by any methodheretofore employed. 1 have overcome this difficulty in severalalternative ways, first, by protecting the resistance with a use formedof the same material but suitably spaced for insulation, second, byinclosing the resistance with a different material of a refractorynature and in which it is hermetically sealed so as to prevent anyaccess of free oxygen to the carbon while under high heat and at thesame time permitting tree transmission of the heat to the work, third,by limiting the tempeinture developed in the resistance to a point belowthat of ignition.

As shown in Fig. 7, the first of the aboife referred to constructions isemployed, that is the inclosingg of the resistance in a case of the sameor similar carbonaceous material, the detail construction being' asfollows:

The protecting case is formed oft an upper and a lower section ll. lleach being provided with outer and inner annular walls ti? and H. Theinner wall. surrounds the chamber in which the work is to be placedwhile the annular space between the -which separates the ends of theresistance from contact with the base ring H of the case and alsopreferably attords side supports to hold the upper portion ot the resistance from contact with the case. The terminal connections for theresistance pass out from the case through an extension thereot which asshown comprises the lateral hollow extension H upon the upper section Hand the re'gis'teringdownwardly extending tubular portion H on thesection ll. llithin these extensions are arranged the terminalconductors l which are suitably fashioned to be maintained out ofcontact with the case and to extend from a bcarin; on the resistance 1to the outlet end of the tube H. The terminals are rigidly attached tothe resistance by a mechanical joint and as shown this consists oil ascrew 1* of the same material as the terminals and the resistance andclampin the same together. The lower end of each terminal suitablysupported in insulating material as indi cated at J. This may be thesame as that employed at J, or if desired a less retractor materia as itwill not be subjected to as high a degree of heat.

lVith the construction thus jl'ar described the case for the resistanceand its cornice tions will. effectually protect the latter fromoxidization as it is evident that bctore oxygen from the atmosphere canobtain access to the heated resistance it must pass through the case,and in so doing will become neutralized by union with the -arbon formingthe carbon monoxid gas. This gas will have no detrimental ctl'cct uponthe resistance whatever tmi'ipcraturc the latter may be h ated to. It ishowever. necessary to protect the case from destruction and also toprovide suitable heat insulation to prevent waste of current. and ameans of access "tor the in sertion and removal of the worl: from theheated chamber. This I accomplish by the use of an external gas-tightjacket which is lined with a refractory heat insulating material and isopen at the bottom in registration. with the chamber ll" to permitaccess to the latter. This case will maintain a nonoxidizing atmosphereabout the resistance and its protecting case for the reason that theheated gases within the case bcing' under higher vapor tension. will notcommingrle by convection with the external atmospheribe ncath. in otherwords. th tendency is for the gases to rise. and where the coldatmosphere beneath the case is tort-ed upward through the orifice in thebottom by any disturbance, it will be expelled without comminglingby thegreater tension of the inner atmosphere.

H is evident from the above description that the outer jacket itgas-tight. above the base, will prevent any exchange ol gases other thanthat by dillusion, which is too slow to produce a detrimental elicct.Upon lll) the first heating of the resistance the oxygen in theatmosphere Within the jacket will at! tack the carbon of the case H butas soon as the supply is exhausted or neutralized, further oxidation isprevented by the gaseous atmosphere thus developed. Thus the resistanceis guarded from injury as long as the protecting case is preserved andthe life of the latter depends on the amount of free oxygen or oxidizinggases contained within the jacket each time that it is heated. Theamount of gas in an empty jacket would produce but a slight oxidizingeffect, but where refractory insulating material is placed within thejacket as a lining this may operate as a holder for'.oxidizing gases,particularly sowwhere there are any carbonates present. I thereforepreferably provide a protection for the case H formed of carbonaceousmaterial preferably pulveriz ed charcoal. This may be placed tocompletely surround the case H without any danger of short ci'rcuitingthe electric circuit, and it is evident that any oxidizing gaspenetrating this material .will be neutralized before it can reach thecarbon case. By the term envelop as employed in the claims is meant.anything that envelops,

whether it be a gas, solid or combination of elements. As shown indetail in Fig. 7, K is a base ring supported on a suitable standard Kand apertured at K for accessto the heater. Upon this ring is mountedthe case H supported by the tubular extensions H, the supports beingheld up a sufficient distance to diminish loss of heat in a downwarddirection to the base. The jacket L is also supported on the ring K andconsists of an outer gas-proof wall L preferably formed of metal, and aninner wall L which may be formed of a more refractory material. Theinner wall is spaced from the jacket H a sufiicient distance for formingthe charcoal containing chamber which preferably connects with a tube Lextending upward to the top of the jacket and provided with a detachablegas-tight cap L.

This permits of renewing the supply of charcoal when necessary. Betweenthe walls L and I isplaced a suitable heat insulating material, such asinfusorial earth, calcined magnesium oxid or other refractorybodieswhich are poor heat conductors.

The terminals I are connected with metallic conductors M which arecoupled by any suitable means (not shown) with the electric circuits.The work-isinserted and withdrawn from the heating chamber H by suitablemeans that shown consisting of a re fractory supporting plate Nconnected/to a vertically extending shank N also of refractory material,and coupled with a slide N upon 'the standard K. The shank N" serves toraise" the support N into the heating chainber,-while the slide Noperated by vention but consisting in the integration of the refractorymaterial which is first in a comminuted state, and in which theresistance is embedded. fected by high heat and is carried to such anextent as to form not only a case but a gasproof seal. Thus the surfaceof the body is either completely fused or is glazed by a more fusiblematerial to form the seal.

Still another modification is shown in Fig. 10 in which the bareresistance I is supported on a refractory insulator base such as H, issurrounded by a jacket L having an inner lining L of a refractorymaterial impervious to the gas and around which the heat insulatingmaterial P is placed. I Vith this construction the work is inserted andremoved from the jacket as in Fig. 7, and upon heating the resistance isexposed to the oxygen within the heating chamber, but as soon as this isneutralized, will be protected by the lining L from further oxidation.The life of such a resistance is necessarily limited but may bemaintained for a sufficient length of time to be of practical service.

Various modifications in the construction of the resistance may be made,as shown in Figs. 11 to 16. Thus in Fig. 11a flat plate Q of graphite isslitted and is provided with terminal connections Q, mechanicallyengaging the same. In Fig. 12 an arch-shaped construction is formed by aslitted segmental plate R, and in Fig. 13 a slitted dome-shapedconstruction S is shown. All of these modifications may be employed aselements in any of the protected constructions referred to andillustrated in Figs. 7, 8 and 10. Fig. 14 illustrates anothermodification which may be employed for a heater of limited length oflife and consists of a spiral resistance T surrounding a mutiie or innercase T and itself surrounded by at protecting case formed of alternatelayers of carbonaceous material and refractory insulating material T andT The spiral is connected at opposite ends to terminal connections Tinsulated from-each other by the layers T of insulating material. Thereis also an outer jackct T with a heat insulating lining T" but notnecessarily a gas-tight construction. With this modification the lengthof'life is limited to the time in which the carbon layers of the outercase remain un- The integration is efconsumed, but during this periodthe resistance will be protected and a high degree of heat may bedeveloped therein.

My invention is applicable to various uses, but is particularly adaptedfor the developof metallic resistances generally employed. Thus in theconstruction shown in Fig. 7 a sufliciently high heat may be developedto fuse platinum silica and other bodies having even a higher fusingpoint, without any detrimental action upon the furnace itself. In factthere is no limit to the degree of the heat except that at which thecarbon vaporizes, as the refractory insulating base may be carried downto a point where it is out of the zone of highest heat. Thus as shown inFig. 15, the resistance may be formed of a slitted cylinder U havingdead ends U extending downward below the poles of the electric currentand supported on an insulating base U An intensely high heat maytherefore be developed within the portions of the graphite forming theelectric circuit, but the temperature of, the lower ends of the bars Uwill be sufficiently low to avoid destroying of the insulatingmaterial.'

lVith the construction as described in use when the current is passedthrough the slitted resistance, heat will be developed first in theresistance and then by radiation will pass to the carbon case which willrise in temperature at near the same speed as the resistance itself.-The outer wall of the case being in contact with the charcoal body willimpart heat to the latter through conduction, and as the ignition pointof the char coal is lower than that of the graphite, the former willfirst be attacked by the oxygen of the atmosphere within the inclosingjacket, this will rapidly convert the free oxygen as well as any carbondioxid which may, be liberated from the heat insulating material intocarbon monoxid, which being fully saturated with carbon will not attackthe graphite resistance or its case. Thus the resistance will beprotected by the gaseous envelop which together with the carbon walls ofthe case effectually excludes any free oxygen. During the period thatthe furnace is under heat, the high vaportension within the heatingchamber and the upper portion of the jacket, will preventany exchange ofatmosphere by convection, and furthermore, the moisture which is alwayspresent in the charcoal and heat insulating material, where the furnaceis used intermittently, will cause a constant slow generation of carbonmonoxid gas and hy drogen by decomposition of the water vapor in contactwith the heated charcoal. This gas will pass out the orifice in the baseof the jacket where-it will be burned, and any oxygen carried into thefurnace by the introduction or withdrawal of work therefrom,

will be; consumed by uniting with this carbon monoxid gas. \Vhenever itis necessary the cap L may be removed and the supply of charcoalsurrounding the graphite case renewed. The charcoal is held from fallingment of high heats above the fusing point out at the base by a retainerwall V of refractory material but at any time when it is desirable toremove the charcoal or any ash accumulating at the bottom of the case,the outer jacket may be lifted off, thereby providing access to all theparts inclosed therein.

lVhile I have shown the resistance with only two terminal connections,it is obvious that intermediate terminals can be extended from the caseto permit of varying the resistance for different voltages and to produce different heating effects.

What I claim as my invention is:

1. An electrical heating unit, comprising a carbon resistor, a carbonshield for protect ing said resistor from atmospheric convection, andmeans for rendering the atmosphere reactively neutral to carbon atcontact temperature.

2. An electrical heating unit, comprising an integral carbon bodyslitted to increase the resistance thereof, a carbon case for protectingsaid resistor from atmospheric convection, an insulator support for saidresistor in said case maintained at relatively high temperature, andmeans for maintaining an atmosphere containing carbon and oxygenreactively neutralto the carbon at contact temperature.

3. An electrical heating unit, comprising an integral carbon resistorbody slitted to increase the resistance thereof, a. carbon case forinclosing said resistor spaced therefrom to maintain atmosphericinsulation, and a refractory insulator support for said resistor withinsaid case.

4. An electrical heating unit. comprising an integral carbon resistorbody slitted to increase the resistance thereof, a carbon case inclosingsaid resistor and spaced therefrom to maintain atmospheric insulation, are fractory insulation forsupporting said re sistor within said case.and means external to said case for developing and maintaining anatmosphere reactively neutral to carbon at contact temperature.

5. An electrical heating unit, comprising an integral carbon bodyvertically slitted to form a series of zigzag sections, a carbon caseinclosing said resistor and spaced therefrom to maintain atmosphericinsulation. a refractory insulator support for said resistor withinsaidcase, engaging the ends of said sections, and means external to thecarbon case for developing and maintaining an. atmosphere reactivelyneutral to carbon at the temperature of contact with said resistor.

6. An electrical heating unit comprising a fashioned in contour slittedcarbon body,

and a protecting gas-tight case therefor forming a chamber open totheexternal atmosphere at a point below the slitted portion of said body.

refractory heat insulating lining. to said jacket, and a carbon bodysurrounding said slitted body and insulated therefrom forming anoxygen-proof shield therefor.

9. An electrical heating unit comprising a fashioned in contour slittedcarbon body, a surrounding gas-proof case therefor, means for developinga non-oxidizing atmosphere within said case enveloping sald body, and arefractory insulating support for said body within said case.

10. An electrical heating unit comprising a fashioned in contour slittedcarbon body forming the resistance element, a carbon case surroundingsaid element and spaced therefrom, a refractory insulator support forsaid resistance element within said case, terminal connections and anextension of said case from which said terminals pass out of the zone ofheat.

11. An electrical heating unit comprising a fashioned'in contour slittedcarbon body of annular form, constituting the resistance element, anannular carbon case mcloslng said body, a refractory insulator supportfor the resistance within said case, and a gasproof jacket surroundingsaid case forming.

' a chamber opened to the external atm'ospher'e in registration withsaid chamber within said annular case.

12. An electrical heating. unit comprising a vertically slitted carbonbody'constituting the resistance element, and a refractory elec-' tricalinsulator support for the lower ends of the sections which are betweenthe slits of said body.

13. An electrical heating unit comprising a slitted carbon body, and aninsulator support for the ends of the sections of said slitted body.

14. An electrical heating unit comprising ,aslitted carbon bodyconstituting the resistance element, means for maintaining a non-voxidizing gaseous atmosphere about said element, and a refractoryinsulator support for said' elementengaging the ends'of the sectionsthereof.

15. An electrical heating unit comprising a slitted carbon bodysurrounding a work chamber and constituting the resistance element, 'agas-proof ja'cket surrounding said resistance element and forming achamber opened at the bottom in registration with said work chamber,means for maintaining a non-oxidizing gas within said jacket andchamber, anda refractory insulator support for the ends of the slittedsections of said body within said jacket.

16. An electrical heatin unit comprising va verticallyslitted-carbon odyconstituting the resistance element, a refractory insu lato-r supportfor the lower ends of the slitted section, and carbon terminalconnections mechanically joined to the ends of said slitted body lead ngoutward therefrom.

17. An electrical heating unit, comprising a combustible resistor, acase surrounding said resistor having an opening thereinv for theinsertion and withdrawal of work, and means for maintaining anon-oxidizing gas surrounding said resistor and. between the same andsaid openin in the case.

18. An electrical ,heatlng unit, comprising 'a combustible resistorarranged to form adj aeent thereto a work chamber, a case surroundingsaid resistor having an opening in its bottom providing access to saidwork chamber for the introduction and withdrawal of work, thermalinsulation interposed between said resistor and case, and means formaintaining a non-oxidizing gas within said work chamber around saidresistor, and between the same and the opening in said case. v

In testimony whereof I afl'tix my signature in presence of twowitnesses.

PRESCOTT M. HULBERT. Witnesses:

JAMES P. BARRY, 'L. J. WHI'ITEMORE.

